Rotor Dynamics and Photoinduced Porosity Switch in Supramolecular Architectures and Covalent Frameworks (Invited Oral presentation)

Organic Porous Materials are an innovative playground for realizing switchable properties such as gas capture and rotor dynamics in the solid state. Recently, photoinduced porous/non-porous reversible interconvertion in a molecular material containing azobenzene-moieites was achieved, showing on/off switch of carbon dioxide adsorption [1]. The combination of porosity with rotor dynamics was achieved in porous organic frameworks PAFs with surface area of 5000 sqm/g [2]. The constructive elements contain rapid rotors, resulting in a dynamic material whose motion can be frozen or released at will by guest species. A first example of molecular rotors in porous molecular crystals will be also presented [3]. The rotors, as fast as 108 Hz at 240 K, are exposed to the crystalline channels, which absorb CO2 and I2 vapors at low pressure. The rotor dynamics could be switched on and off by I2 vapors, suggesting the use of molecular crystals in sensing and pollutant management. Crystals with permanent porosity were exploited in an unusual way to decorate crystal surfaces with regular arrays of dipolar rotors. The inserted molecules carry alkyl chains which are included as guests into the channel-ends [4]. The rotors stay at the surface due to a bulky molecular stopper which prevents the rotors from entering the channels. The host-guest relationships were established by 2D solid-state NMR and low rotational barriers were found by dielectric spectroscopy. Recently, fast rotating organic elements bearing carbon-fluorine dipoles have been fabricated in porous organic-inorganic hybrid structures [5]. The reactivity of the pivot bonds allowed halogen addition and motion regulation. [1] Nature Chem. 2015, accepted; [2] Angew. Chem. Int. Ed. 2014, 53, 1043; [3] J. Am. Chem. Soc. 2014, 136, 618; [4] J. Am. Chem. Soc. 2012, 134, 10122; [5] Angew. Chemie Int. Ed. 2015, (Front Cover and VIP paper).